Improving rate and the search for improved efficiency are constant preoccupations of mechanical watch designers, who seek to obtain the greatest possible power reserve, combined with regularity, precision and security in the most difficult conditions of use. The regulating assembly and the escape mechanism are at the heart of this problem.
In particular, in mechanical watches, escapements have to satisfy several safety criteria. One of the safety devices, the anti-trip mechanism, is designed to prevent the angular extension of the balance going beyond a normal angle of rotation.
EP Patent No 1801668 B1 in the name of Montres Breguet SA proposes a mechanism whose structure is characterized in that it includes a pinion mounted on the balance staff. This pinion meshes with a toothed wheel, at least one radius of which abuts against a fixed stop if the balance is driven beyond its normal angle of rotation. However, this mechanism affects the inertia of the balance and may disturb its oscillations. Further, there is friction in the gear forming the mechanism which also disturbs the regulating mechanism.
EP Patent Application No 1 666990 A2 in the name of Montres Breguet SA discloses another anti-trip mechanism based on the expansion of the balance spring: a locking arm, fixed to the outer coil of the balance spring, is inserted between a finger integral with the balance and two columns integral with the balance bar. Locking only occurs in the event of excessive expansion of the balance spring beyond an angle exceeding its normal operating angle. This mechanism only limits the angle of rotation in one direction of rotation.
In short, known safety mechanisms each have at least one of the recurrent drawbacks: disruption of the oscillations by modifying the inertia of the regulating member, adversely affecting efficiency under the effect of friction, or limiting the angle of rotation in only one direction of rotation.
EP Patent Application No 2450756 A1 in the name of Nivarox discloses an anti-trip device for an escapement mechanism, with a pivoting mobile component carrying a finger which moves in a cam path integral with the balance. This pivoting mobile component may include an arm with a bistable lever, particularly an elastic bistable lever.
EP Patent Application No 2037335 A2 in the name of Enzler-Von-Gunten discloses a pallet lever which has two arms provided with pallet stones, and a pallet fork, the assembly being formed in a single piece with two flexible securing arms, which define a virtual pivot axis of the pallet lever, and allow the pallet lever to pivot when they bend, the median axes of these two strips intersecting on the virtual axis.
The international application No WO2011/120 180 A1 in the name of ROLEX describes a blocking device for an escapement wheel. This device includes a blocker with two pallets bound with a structure via two elastic blades in order to define a virtual pivot. A third elastic blade acts laterally on this blocker.
The Swiss Patent Application No CH 703 333 A2 in the name of FRAGNIERE discloses an anchor with a bistable return spring fixed on the lever of the anchor between the fork and the pivot axis.
EP Patent Application No 1 710 636 A1 in the name of ROCHAT describes a mechanism similar to a detent escapement, with a draw system including a bistable spring.
EP Patent Application No 2 450 757 A1 in the name of NIVAROX describes an antitripping mechanism for an escapement mechanism with a bistable component including amplitude limitation means active against shocks.
The international application No WO 2013/144236 in the name of NIVAROX describes a flexible escapement mechanism with a mobile frame carried by bistable flexible blades.